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Does Math Need Rules

Gravity Assist1:13

Transcription

We know that math has rules.

But do you know why?

What happens when you divide by zero? Suddenly, 1 = 2. If A = B and we multiply both sides by A, we'll have this. Subtract B squared from both sides. Now, pull both sides apart. Factor the left, factor the right. We have an exact match. A minus B on both sides. Cancel it out. Wipe it off the board. What do we have? A + B = B. But remember our first rule, A = B. So, replace A with B. B + B = B. 2B = B. Divide by B. 2 = 1.

Every single step looks flawless. So, where did the math break? Look at this line. We canceled out A minus B. But since A = B, A minus B is zero. So, we divided by zero.

But why does that break math? Why is it illegal? Division is just reverse multiplication. 10 / 2 is 5 because 5 * 2 is 10. So, what is 0 / 0? What number multiplied by zero equals zero? The answer is every number. 5 * 0 is zero. A million times zero is zero. So, 0 / 0 is every number.